dpll: docs: add support for pin signal phase offset/adjust

Add documentation on:
- measurement of phase of signal between pin and dpll
- adjustment of pin signal phase

Signed-off-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/driver-api/dpll.rst

@@ -173,6 +173,47 @@ in order to configure active input of a MUX-type pin, the user needs to
 request desired pin state of the child pin on the parent pin,
 as described in the ``MUX-type pins`` chapter.
 
+Phase offset measurement and adjustment
+========================================
+
+Device may provide ability to measure a phase difference between signals
+on a pin and its parent dpll device. If pin-dpll phase offset measurement
+is supported, it shall be provided with ``DPLL_A_PIN_PHASE_OFFSET``
+attribute for each parent dpll device.
+
+Device may also provide ability to adjust a signal phase on a pin.
+If pin phase adjustment is supported, minimal and maximal values that pin
+handle shall be provide to the user on ``DPLL_CMD_PIN_GET`` respond
+with ``DPLL_A_PIN_PHASE_ADJUST_MIN`` and ``DPLL_A_PIN_PHASE_ADJUST_MAX``
+attributes. Configured phase adjust value is provided with
+``DPLL_A_PIN_PHASE_ADJUST`` attribute of a pin, and value change can be
+requested with the same attribute with ``DPLL_CMD_PIN_SET`` command.
+
+  =============================== ======================================
+  ``DPLL_A_PIN_ID``               configured pin id
+  ``DPLL_A_PIN_PHASE_ADJUST_MIN`` attr minimum value of phase adjustment
+  ``DPLL_A_PIN_PHASE_ADJUST_MAX`` attr maximum value of phase adjustment
+  ``DPLL_A_PIN_PHASE_ADJUST``     attr configured value of phase
+                                  adjustment on parent dpll device
+  ``DPLL_A_PIN_PARENT_DEVICE``    nested attribute for requesting
+                                  configuration on given parent dpll
+                                  device
+    ``DPLL_A_PIN_PARENT_ID``      parent dpll device id
+    ``DPLL_A_PIN_PHASE_OFFSET``   attr measured phase difference
+                                  between a pin and parent dpll device
+  =============================== ======================================
+
+All phase related values are provided in pico seconds, which represents
+time difference between signals phase. The negative value means that
+phase of signal on pin is earlier in time than dpll's signal. Positive
+value means that phase of signal on pin is later in time than signal of
+a dpll.
+
+Phase adjust (also min and max) values are integers, but measured phase
+offset values are fractional with 3-digit decimal places and shell be
+divided with ``DPLL_PIN_PHASE_OFFSET_DIVIDER`` to get integer part and
+modulo divided to get fractional part.
+
 Configuration commands group
 ============================
 
@@ -263,15 +304,23 @@ according to attribute purpose.
                                        frequencies
       ``DPLL_A_PIN_ANY_FREQUENCY_MIN`` attr minimum value of frequency
       ``DPLL_A_PIN_ANY_FREQUENCY_MAX`` attr maximum value of frequency
+    ``DPLL_A_PIN_PHASE_ADJUST_MIN``    attr minimum value of phase
+                                       adjustment
+    ``DPLL_A_PIN_PHASE_ADJUST_MAX``    attr maximum value of phase
+                                       adjustment
+    ``DPLL_A_PIN_PHASE_ADJUST``        attr configured value of phase
+                                       adjustment on parent device
     ``DPLL_A_PIN_PARENT_DEVICE``       nested attr for each parent device
                                        the pin is connected with
       ``DPLL_A_PIN_PARENT_ID``         attr parent dpll device id
       ``DPLL_A_PIN_PRIO``              attr priority of pin on the
                                        dpll device
       ``DPLL_A_PIN_STATE``             attr state of pin on the parent
                                        dpll device
-     ``DPLL_A_PIN_DIRECTION``          attr direction of a pin on the
+      ``DPLL_A_PIN_DIRECTION``         attr direction of a pin on the
                                        parent dpll device
+      ``DPLL_A_PIN_PHASE_OFFSET``      attr measured phase difference
+                                       between a pin and parent dpll
     ``DPLL_A_PIN_PARENT_PIN``          nested attr for each parent pin
                                        the pin is connected with
       ``DPLL_A_PIN_PARENT_ID``         attr parent pin id
@@ -284,6 +333,8 @@ according to attribute purpose.
   ``DPLL_CMD_PIN_SET``                 command to set pins configuration
     ``DPLL_A_PIN_ID``                  attr unique a pin ID
     ``DPLL_A_PIN_FREQUENCY``           attr requested frequency of a pin
+    ``DPLL_A_PIN_PHASE_ADJUST``        attr requested value of phase
+                                       adjustment on parent device
     ``DPLL_A_PIN_PARENT_DEVICE``       nested attr for each parent dpll
                                        device configuration request
       ``DPLL_A_PIN_PARENT_ID``         attr parent dpll device id